I have collected all of the missing Exos but the triumph still says that I am missing one. I had to check the lore to see if I am missing one and it seems that the one I am missing is the Exo that's in the "Creation" sector right next to Clovis. The Lore of the missing Exo is "Noe-2".
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I’m having the same issue. Collected all exos and no triumph